Method and apparatus for monitoring rotational position of an electric machine

Abstract

A method for monitoring an electric motor employing a pulse-type rotational position sensor includes monitoring a signal output from the pulse-type rotational position sensor and a reference signal associated with a control signal for the electric motor. A position of a rotor of the electric motor coincident with the reference signal is determined based upon a nominal rotor position, a nominal rotational speed of the rotor and a time between the reference signal and a falling edge of the signal output from the pulse-type rotational position sensor. The electric motor is controlled based upon the position of the rotor.

The invention claimed is: 
     
       1. A method for monitoring an electric motor employing a pulse-type rotational position sensor, comprising:
 monitoring a signal output from the pulse-type rotational position sensor and a reference signal associated with a control signal for the electric motor; 
 determining a position of a rotor of the electric motor coincident with the reference signal based upon a nominal rotor position, a nominal rotational speed of the rotor and a time between the reference signal and a falling edge of the signal output from the pulse-type rotational position sensor; and 
 controlling the electric motor based upon the position of the rotor. 
 
     
     
       2. The method of  claim 1 , wherein determining the position of the rotor coincident with the PWM reference signal comprises determining the position of the rotor in accordance with the following relationship:
   θ Final   [k]=θ   MT   [k]+ω   MT   [k− 1 ]×ΔT[k] 
 
 wherein
 θ Final [k] is the position of the rotor, 
 θ MT [k] is the nominal rotor position, 
 ω MT [k−1] is the nominal rotational speed of the rotor, and 
 ΔT[k] is the time between the reference signal to the falling edge of the signal output from the pulse-type rotational position sensor. 
 
 
     
     
       3. The method of  claim 1 , wherein the nominal rotational speed of the rotor is determined in accordance with the following relationship: 
       
         
           
             
               
                 ω 
                 MT 
               
               = 
               
                 
                   m 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                   * 
                   α 
                 
                 
                   Ppr 
                   ⁡ 
                   
                     ( 
                     
                       Tsp 
                       + 
                       
                         Δ 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         T 
                       
                     
                     ) 
                   
                 
               
             
           
         
         wherein
 ω MT  is the nominal rotational speed 
 Tsp is a sampling period, 
 m1 is a discrete quantity of sensor pulses during the sampling period Tsp, said sensor pulses comprising the signal output from the pulse-type rotational position sensor, 
 α is a rotational angle of the rotor between two adjacent sensor pulses, 
 ΔT is an elapsed time that is a difference between a fixed time interval and the sampling period Tsp, and 
 Ppr is a resolution of an encoder of the pulse-type rotational position sensor. 
 
       
     
     
       4. The method of  claim 1 , wherein monitoring the reference signal associated with the control signal for the electric motor comprises monitoring a PWM reference signal indicating completion of one cycle of signals for controlling power flow to the electric motor. 
     
     
       5. The method of  claim 1 , wherein monitoring the signal output from the pulse-type rotational position sensor comprises monitoring signal output from an edge-sensing device comprising a magnetoresistive sensor including a stationary sensing element mounted on the stator of the electric motor, said magnetoresistive sensor monitoring an encoder mounted on a shaft of the rotor of the electric motor. 
     
     
       6. The method of  claim 1 , wherein monitoring the signal output from the pulse-type rotational position sensor comprises monitoring signal output from an edge-sensing device comprising a digital Hall-effect sensor including a stationary sensing element mounted on the stator of the electric motor, said digital Hall-effect sensor monitoring an encoder mounted on a shaft of the rotor of the electric motor. 
     
     
       7. A method for monitoring a multi-phase electric machine including an inverter generating pulsewidth-modulation signals for controlling power flow to generate torque, the electric machine employing a low-resolution pulse-type rotational position sensor for positional feedback, comprising:
 monitoring a signal output from the low-resolution pulse-type rotational position sensor and a reference signal associated with a control signal for the electric machine originating from the inverter; 
 determining a position of a rotor of the electric machine coincident with the reference signal based upon a nominal rotor position, a nominal rotational speed of the rotor and a time between the reference signal and a signal output from the low-resolution pulse-type rotational position sensor; and 
 controlling the electric machine based upon the position of the rotor. 
 
     
     
       8. The method of  claim 7 , wherein determining a position of the rotor coincident with the PWM reference signal comprises determining the position of the rotor in accordance with the following relationship:
   θ Final   [k]=θ   MT   [k]+ω   MT   [k− 1 ]×ΔT[k] 
 
 wherein
 θ Final [k] is the position of the rotor, 
 θ MT [k] is the nominal rotor position, 
 ω MT [k−1] is the nominal rotational speed of the rotor, and 
 ΔT[k] is the time from the reference signal to the signal output from the low-resolution pulse-type rotational position sensor. 
 
 
     
     
       9. The method of  claim 7 , wherein the nominal rotational speed of the rotor is determined in accordance with the following relationship: 
       
         
           
             
               
                 ω 
                 MT 
               
               = 
               
                 
                   m 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                   * 
                   α 
                 
                 
                   Ppr 
                   ⁡ 
                   
                     ( 
                     
                       Tsp 
                       + 
                       
                         Δ 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         T 
                       
                     
                     ) 
                   
                 
               
             
           
         
         wherein
 ω MT  is the nominal rotational speed of the rotor 
 Tsp is a nominal sampling period, 
 m1 is a discrete quantity of sensor pulses during the sampling period Tsp, said sensor pulses comprising the signal output from the low-resolution pulse-type rotational position sensor, 
 α is a rotational angle of the rotor between two of adjacent sensor pulses, 
 ΔT is an elapsed time that is a difference between a fixed time interval and the nominal sampling period Tsp, and 
 Ppr is a resolution of an encoder of the low-resolution pulse-type rotational position sensor. 
 
       
     
     
       10. The method of  claim 7 , wherein monitoring the reference signal associated with the control signal for the electric machine comprises monitoring a PWM reference signal indicating completion of one cycle of signals for controlling power flow to the electric machine. 
     
     
       11. The method of  claim 7 , wherein monitoring the signal output from the low-resolution pulse-type rotational position sensor comprises monitoring signal output from a magnetoresistive sensor including a stationary sensing element mounted on the stator of the electric machine, said magnetoresistive sensor monitoring a low-resolution encoder mounted on a shaft of the rotor of the electric machine. 
     
     
       12. The method of  claim 7 , wherein monitoring the signal output from the low-resolution pulse-type rotational position sensor comprises monitoring signal output from an edge-sensing device comprising a digital Hall-effect sensor including a stationary sensing element mounted on the stator of the electric machine, said digital Hall-effect sensor monitoring a low-resolution encoder mounted on a shaft of the rotor of the electric machine.